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Message-ID: <k5h7tto6kdwcgtxoeglqncojjwact6xxqnin4inffol74jdows@fj5ujezqwb24>
Date: Fri, 12 Jul 2024 00:18:47 +0530
From: Amit Machhiwal <amachhiw@...ux.ibm.com>
To: Lizhi Hou <lizhi.hou@....com>
Cc: Bjorn Helgaas <helgaas@...nel.org>, linux-pci@...r.kernel.org,
linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
kvm-ppc@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
Rob Herring <robh@...nel.org>, Vaibhav Jain <vaibhav@...ux.ibm.com>,
Nicholas Piggin <npiggin@...il.com>,
Michael Ellerman <mpe@...erman.id.au>,
Vaidyanathan Srinivasan <svaidy@...ux.ibm.com>,
Kowshik Jois B S <kowsjois@...ux.ibm.com>,
Lukas Wunner <lukas@...ner.de>
Subject: Re: [PATCH] PCI: Fix crash during pci_dev hot-unplug on pseries KVM
guest
On 2024/07/10 09:48 PM, Lizhi Hou wrote:
>
> On 7/5/24 12:20, Bjorn Helgaas wrote:
> > [+cc Lukas, FYI]
> >
> > On Wed, Jul 03, 2024 at 07:46:34PM +0530, Amit Machhiwal wrote:
> > > With CONFIG_PCI_DYNAMIC_OF_NODES [1], a hot-plug and hot-unplug sequence
> > > of a PCI device attached to a PCI-bridge causes following kernel Oops on
> > > a pseries KVM guest:
> > >
> > > RTAS: event: 2, Type: Hotplug Event (229), Severity: 1
> > > Kernel attempted to read user page (10ec00000048) - exploit attempt? (uid: 0)
> > > BUG: Unable to handle kernel data access on read at 0x10ec00000048
> > > Faulting instruction address: 0xc0000000012d8728
> > > Oops: Kernel access of bad area, sig: 11 [#1]
> > > LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
> > > <snip>
> > > NIP [c0000000012d8728] __of_changeset_entry_invert+0x10/0x1ac
> > > LR [c0000000012da7f0] __of_changeset_revert_entries+0x98/0x180
> > > Call Trace:
> > > [c00000000bcc3970] [c0000000012daa60] of_changeset_revert+0x58/0xd8
> > > [c00000000bcc39c0] [c000000000d0ed78] of_pci_remove_node+0x74/0xb0
> > > [c00000000bcc39f0] [c000000000cdcfe0] pci_stop_bus_device+0xf4/0x138
> > > [c00000000bcc3a30] [c000000000cdd140] pci_stop_and_remove_bus_device_locked+0x34/0x64
> > > [c00000000bcc3a60] [c000000000cf3780] remove_store+0xf0/0x108
> > > [c00000000bcc3ab0] [c000000000e89e04] dev_attr_store+0x34/0x78
> > > [c00000000bcc3ad0] [c0000000007f8dd4] sysfs_kf_write+0x70/0xa4
> > > [c00000000bcc3af0] [c0000000007f7248] kernfs_fop_write_iter+0x1d0/0x2e0
> > > [c00000000bcc3b40] [c0000000006c9b08] vfs_write+0x27c/0x558
> > > [c00000000bcc3bf0] [c0000000006ca168] ksys_write+0x90/0x170
> > > [c00000000bcc3c40] [c000000000033248] system_call_exception+0xf8/0x290
> > > [c00000000bcc3e50] [c00000000000d05c] system_call_vectored_common+0x15c/0x2ec
> > > <snip>
> > >
> > > A git bisect pointed this regression to be introduced via [1] that added
> > > a mechanism to create device tree nodes for parent PCI bridges when a
> > > PCI device is hot-plugged.
> > >
> > > The Oops is caused when `pci_stop_dev()` tries to remove a non-existing
> > > device-tree node associated with the pci_dev that was earlier
> > > hot-plugged and was attached under a pci-bridge. The PCI dev header
> > > `dev->hdr_type` being 0, results a conditional check done with
> > > `pci_is_bridge()` into false. Consequently, a call to
> > > `of_pci_make_dev_node()` to create a device node is never made. When at
> > > a later point in time, in the device node removal path, a memcpy is
> > > attempted in `__of_changeset_entry_invert()`; since the device node was
> > > never created, results in an Oops due to kernel read access to a bad
> > > address.
> > >
> > > To fix this issue the patch updates `pci_stop_dev()` to ensure that a
> > > call to `of_pci_remove_node()` is only made for pci-bridge devices.
> > >
> > > [1] commit 407d1a51921e ("PCI: Create device tree node for bridge")
> > >
> > > Fixes: 407d1a51921e ("PCI: Create device tree node for bridge")
> > > Reported-by: Kowshik Jois B S <kowsjois@...ux.ibm.com>
> > > Tested-by: Kowshik Jois B S <kowsjois@...ux.ibm.com>
> > > Signed-off-by: Amit Machhiwal <amachhiw@...ux.ibm.com>
> > Thanks for the patch and testing! Would like a reviewed-by from
> > Lizhi.
>
> of_pci_make_dev_node() will create of nodes for some endpoint devices (not a
> bridge) as well. And actually this is the main purpose.
>
> Maybe the patch as below would resolve the Oops?
Thanks for the patch, Lizhi! I tried out this patch and don't see the issue with
the same. The hot-plug and hot-unplug of PCI device seem to work fine as
expected.
~ Amit
>
> diff --git a/drivers/of/dynamic.c b/drivers/of/dynamic.c
> index dda6092e6d3a..3c693b091ecf 100644
> --- a/drivers/of/dynamic.c
> +++ b/drivers/of/dynamic.c
> @@ -492,21 +492,29 @@ struct device_node *__of_node_dup(const struct
> device_node *np,
> * a given changeset.
> *
> * @ocs: Pointer to changeset
> + * @np: Pointer to device node. If it is not null, init it directly instead
> of
> + * allocate a new node.
> * @parent: Pointer to parent device node
> * @full_name: Node full name
> *
> * Return: Pointer to the created device node or NULL in case of an error.
> */
> struct device_node *of_changeset_create_node(struct of_changeset *ocs,
> + struct device_node *np,
> struct device_node *parent,
> const char *full_name)
> {
> - struct device_node *np;
> int ret;
>
> - np = __of_node_dup(NULL, full_name);
> - if (!np)
> - return NULL;
> + if (!np) {
> + np = __of_node_dup(NULL, full_name);
> + if (!np)
> + return NULL;
> + } else {
> + of_node_set_flag(np, OF_DYNAMIC);
> + of_node_set_flag(np, OF_DETACHED);
> + }
> +
> np->parent = parent;
>
> ret = of_changeset_attach_node(ocs, np);
> diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
> index 445ad13dab98..087de26852cc 100644
> --- a/drivers/of/unittest.c
> +++ b/drivers/of/unittest.c
> @@ -871,7 +871,7 @@ static void __init of_unittest_changeset(void)
> unittest(!of_changeset_add_property(&chgset, parent, ppadd), "fail
> add prop prop-add\n");
> unittest(!of_changeset_update_property(&chgset, parent, ppupdate),
> "fail update prop\n");
> unittest(!of_changeset_remove_property(&chgset, parent, ppremove),
> "fail remove prop\n");
> - n22 = of_changeset_create_node(&chgset, n2, "n22");
> + n22 = of_changeset_create_node(&chgset, NULL, n2, "n22");
> unittest(n22, "fail create n22\n");
> unittest(!of_changeset_add_prop_string(&chgset, n22, "prop-str",
> "abcd"),
> "fail add prop prop-str");
> diff --git a/drivers/pci/of.c b/drivers/pci/of.c
> index 51e3dd0ea5ab..92c079b2e570 100644
> --- a/drivers/pci/of.c
> +++ b/drivers/pci/of.c
> @@ -608,18 +608,28 @@ int devm_of_pci_bridge_init(struct device *dev, struct
> pci_host_bridge *bridge)
>
> #ifdef CONFIG_PCI_DYNAMIC_OF_NODES
>
> +void of_pci_free_node(struct device_node *np)
> +{
> + struct of_changeset *cset;
> +
> + cset = (struct of_changeset *)(np + 1);
> +
> + np->data = NULL;
> + of_changeset_revert(cset);
> + of_changeset_destroy(cset);
> + of_node_put(np);
> +}
> +
> void of_pci_remove_node(struct pci_dev *pdev)
> {
> struct device_node *np;
>
> np = pci_device_to_OF_node(pdev);
> - if (!np || !of_node_check_flag(np, OF_DYNAMIC))
> + if (!np || np->data != of_pci_free_node)
> return;
> pdev->dev.of_node = NULL;
>
> - of_changeset_revert(np->data);
> - of_changeset_destroy(np->data);
> - of_node_put(np);
> + of_pci_free_node(np);
> }
>
> void of_pci_make_dev_node(struct pci_dev *pdev)
> @@ -655,14 +665,18 @@ void of_pci_make_dev_node(struct pci_dev *pdev)
> if (!name)
> return;
>
> - cset = kmalloc(sizeof(*cset), GFP_KERNEL);
> - if (!cset)
> + np = kzalloc(sizeof(*np) + sizeof(*cset), GFP_KERNEL);
> + if (!np)
> goto out_free_name;
> + np->full_name = name;
> + of_node_init(np);
> +
> + cset = (struct of_changeset *)(np + 1);
> of_changeset_init(cset);
>
> - np = of_changeset_create_node(cset, ppnode, name);
> + np = of_changeset_create_node(cset, np, ppnode, NULL);
> if (!np)
> - goto out_destroy_cset;
> + goto out_free_node;
>
> ret = of_pci_add_properties(pdev, cset, np);
> if (ret)
> @@ -672,9 +686,8 @@ void of_pci_make_dev_node(struct pci_dev *pdev)
> if (ret)
> goto out_free_node;
>
> - np->data = cset;
> + np->data = of_pci_free_node;
> pdev->dev.of_node = np;
> - kfree(name);
>
> return;
>
> diff --git a/include/linux/of.h b/include/linux/of.h
> index a0bedd038a05..f774459d0d84 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -1631,6 +1631,7 @@ static inline int of_changeset_update_property(struct
> of_changeset *ocs,
> }
>
> struct device_node *of_changeset_create_node(struct of_changeset *ocs,
> + struct device_node *np,
> struct device_node *parent,
> const char *full_name);
> int of_changeset_add_prop_string(struct of_changeset *ocs,
>
> Thanks,
>
> Lizhi
>
> >
> > > ---
> > > drivers/pci/remove.c | 3 ++-
> > > 1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/pci/remove.c b/drivers/pci/remove.c
> > > index d749ea8250d6..4e51c64af416 100644
> > > --- a/drivers/pci/remove.c
> > > +++ b/drivers/pci/remove.c
> > > @@ -22,7 +22,8 @@ static void pci_stop_dev(struct pci_dev *dev)
> > > device_release_driver(&dev->dev);
> > > pci_proc_detach_device(dev);
> > > pci_remove_sysfs_dev_files(dev);
> > > - of_pci_remove_node(dev);
> > > + if (pci_is_bridge(dev))
> > > + of_pci_remove_node(dev);
> > IIUC, this basically undoes the work that was done by
> > of_pci_make_dev_node().
> >
> > The call of of_pci_make_dev_node() from pci_bus_add_device() was added
> > by 407d1a51921e and is conditional on pci_is_bridge(), so it makes
> > sense to me that the remove needs a similar condition.
> >
> > > pci_dev_assign_added(dev, false);
> > > }
> > >
> > > base-commit: e9d22f7a6655941fc8b2b942ed354ec780936b3e
> > > --
> > > 2.45.2
> > >
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